For co-manipulation involving humans and robots, robot controllers that are based on human-human behavior should allow more comfortable and coordinated movement between the human-robot dyad. In this paper, we describe an experiment between human-human dyads where we recorded the force and motion data as leader-follower dyads moved in translation and rotation. The force/motion data was then analyzed for patterns found during lateral translation only. For extended objects, lateral translation and in-place rotation are ambiguous, but this paper determines a way to characterize lateral translation triggers for future use in human-robot interaction. The study has 4 main results. First, interaction forces are non-negligible and are necessary for co-manipulation. Second, minimum-jerk trajectories are found in the lateral direction only for lateral movement. Third, the beginning of a lateral movement is characterized by distinct force triggers by the leader. Fourth, there are different metrics that can be calculated to determine which dyads moved most effectively in the lateral direction.